The present invention concerns the technical field of wristwatches and, more particularly, that of wristwatches including a case provided with a first electric conductor, and an electric circuit connected to the first electric conductor, and a wristband including a second electric conductor.
With reference to FIG. 1 of the present description, European Patent No. 0 186 804 discloses a wristwatch 1 including a case 3 and a wristband 5 associated with said case. Case 3 includes an electric circuit 7 provided with an integrated circuit (not shown in FIG. 1) and a display device 9, case 3 being sealed by a crystal 11. Wristband 5 includes two strips 12a and 12b formed of a flexible plastic material, and a conductor 24a arranged between these two strips. Strip 12a includes a thick zone 26, of bulged shape in which is arranged a transverse opening 27 intended to accommodate a pin 28 by means of which wristband 5 is hinged to case 3.
One problem encountered with wristwatch 1 lies in forming an electric connection between electric circuit 7 of case 3 and conductor 24a of wristband 5.
The solution according to European Patent No. 0 186 804 consists in forming an electric connection via mechanical contact between electric circuit 7 and conductor 24a. Thus, wristwatch 1 includes a junction device 13 including a set of contact elements 15 formed by a rigid conductive element 17, an elastic conductive element 19, and a cylindrical slug 21, these components being arranged to form the electric connection between conductor 24a and integrated circuit 7.
However, an electric connection of this type has several drawbacks. An alteration in this electric connection can occur due to sealing problems (in particular oxidation of the junction device components) and during maintenance of the wristwatch (in particular during replacement of the wristband by a new wristband).
Another drawback of wristwatch 1 lies in the fact that the rotation of wristband 5 about pin 28 of case 3 is limited, because of the presence of junction device 13 which is fixed with respect to the case, which limits the comfort of the wearer of wristwatch 1.
Another drawback of wristwatch 1 lies in the fact that the choice of materials used to form case 3 is limited to achieve electric insulation of the electric connection between integrated circuit 7 and conductor 24a. 
U.S. Pat. No. 5,159,713 discloses a wristwatch with a communication device for transmitting and receiving messages, such as a pager. FIGS. 12a to 12c of this document show that the watch wristband includes a metal strip extended over the entire length of the wristband and forming an antenna for the message transmitting and receiving device.
The ends of the metal strip are each connected in electric and mechanical contact to a metal pin hinging the wristband to the watch case.
The metal ends of the pin each rest in a metal articulation housing of the watch case forming an electric connection between the wristband antenna and the electronic circuit housed in the case.
Drawbacks of this design lie on the one hand in the fact that the mechanical contact between the pin and its housing also has to assure the electric connection between the antenna and the electronic circuit, and on the other hand as regards the articulation pin, when the wristband is changed. The contact metal parts of the pin and its housing can oxidise in a damp atmosphere or suffer damage capable of modifying the electric contact resistance which can affect the impedance value from the antenna to the electronic circuit.
Instead of assuring the electric connection in a resistive manner via mechanical contact between two contact pads, one can envisage assuring said connection using a capacitive coupling which avoids the aforecited drawbacks.
One example of such a connection by capacitive coupling is disclosed in U.S. Pat. No. 5,170,173 which concerns the field of communication devices, such as wireless portable telephones. The hinge between the portion of the microphone and the main body is provided with two coupling capacitors to electrically connect each end of the antenna arranged in the microphone portion. Two embodiments are described wherein the coupling capacitors are either capacitors with a plane circular plate arranged perpendicular to the articulation pin with a dielectric between the plates, or tubular capacitors arranged radially along the articulation pin with a dielectric between the metal tubes.
It is to be noted that, whatever the position of the microphone portion with respect to the main body, the capacitances do not change value.
Hinges of this type for mobile telephones are of significant dimensions which does not pose a problem for housing capacitors in the form of circular or tubular plates therein. Moreover, the telephone case is made of plastic material which makes it easy to inlay connection wires to the plates or tubes of the coupling capacitors, for example by moulding. However, providing such an arrangement in the case of a metal case is not envisaged, since the shape of the capacitors would have to change significantly.
An arrangement of this type in a wristwatch can cause certain drawbacks, as indicated above, when the articulation pin is used as means for providing an electric connection with an electronic circuit in the case. Moreover, in the watchmaking industry, space requirement and rationalisation are important parameters for an arrangement of this type as a function particularly of production costs and the facility with which a watch wristband can be changed.
An object of the present invention is to provide a wristwatch including a case provided with a first electric conductor arranged in the vicinity of a first outer surface of the case and an electric circuit connected to the first electric conductor, and a wristband including a second electric conductor arranged in the vicinity of a second outer surface of the wristband, said first and second conductors being arranged to establish an electric connection by capacitive coupling while overcoming the aforementioned drawbacks.
Another object of the present invention is to provide a wristwatch of this type arranged to prevent any alteration in the electric connection between the first and second electric conductors.
Another object of the present invention is to provide a wristwatch of this type wherein the arrangement of the electric connection makes replacing the wristband easy.
Another object of the present invention is to provide a wristwatch of this type wherein the arrangement of the electric connection does not limit the movement of the wristband with respect to the case, in order to improve the comfort of the wristwatch wearer.
Another object of the present invention is to provide a wristwatch of this type wherein the arrangement of the electric connection does not limit the choice of materials used to form the case.
Another object of the present invention is to provide a wristwatch answering the usual concerns as to space requirement and rationality in a horological application.
Another object of the present invention is to provide a wristwatch answering the usual concern in the industry, as to the cost.
These objects, in addition to others, are achieved by the wristwatch according to claim 1.
One advantage of the arrangement of the first and second conductors of such a wristwatch is that an electric connection without any mechanical contact is made and, more precisely, by a capacitive coupling between the first conductor of the case and the second conductor of the wristband, which does not require any additional external material arrangement other than the conventional articulation between the wristband and the case.
Another advantage of such an arrangement of the first and second conductors is that it avoids limiting the movement of the wristband with respect to the case, as is the case in conventional wristwatches, because of the presence of a mechanical or galvanic contact between the first conductor of the case and the second conductor of the wristband.
Another advantage of such an arrangement of the first and second conductors is that it facilitates replacement of the wristband by another similar wristband, without there being any material deterioration in the electric connection between the first conductor of the case and the second conductor of the wristband, following such replacement.